How to Justify the Symmetrization Postulate in Quantum Mechanics

The aim of this paper is to reconstruct and correct one argument (known in the literature as the exchange degeneracy argument) in support of the symmetrization postulate in quantum mechanics. I identify the central premise of the argument as a thesis specifying a particular ontic (or epistemic) property of quantum superpositions. The precise form of this thesis depends on some underlying assumptions of a metaphysical character (concerning identifications of objects across possible worlds, or representations de re). I compare the exchange degeneracy argument with alternative formal arguments for the symmetrization postulate, and I discuss the role and meaning of labels in the symmetric/antisymmetric representations of the states of many particles.